Composite sheet used for artificial leather with low elongation and excellent softness

ABSTRACT

A composite sheet used for artificial leather with low elongation and excellent softness which includes a non-woven fabric layer, a woven or knitted fabric layer and a polyurethane resin, wherein the non-woven fabric layer and the woven or knitted fabric layer are entangled with each other.

This application is a Continuation of co-pending Application Ser. No.10/501,910, now U.S. Pat. No. 7,820,569, filed on Jul. 20, 2004 and forwhich priority is claimed under 35 U.S.C. §120. Application Ser. No.10/501,910 is the national phase of PCT International Application No.PCT/KR03/00204 filed on Jan. 29, 2003 under 35 U.S.C. §371. The entirecontents of each of the above-identified applications are herebyincorporated by reference.

TECHNICAL FIELD

The present invention relates to a composite sheet used for artificialleather with low elongation and excellent softness. More particularly,the present invention relates to a composite sheet used for artificialleather which is useful for the production of artificial leather forfurniture, cars, men's clothing and sundry goods because it has anexcellent form-stability and a soft touch.

An artificial leather is generally produced by coating resin on thesurface of a sheet for artificial leather consisting of two components,i.e., non-woven fabric made of ultra fine fibers and polyurethane resinaccording to its uses or directly dyeing the surface.

The above-mentioned sheet for artificial leather is produced by a methodcomprising the steps of: (i) forming a composite fiber capable ofbecoming fine into a web by a carding-cross lapping process; (ii)needle-punching the web to form a non-woven fabric; (iii) making thefiber ultra fine by impregnating the non-woven fabric with polyurethaneresin and extracting and removing the sea component of the compositefiber or by firstly extracting and removing the sea component of thecomposite fiber and then impregnating the non-woven fabric withpolyurethane resin; and (iv) buffing the fabric to form raised fibers onthe surface.

BACKGROUND ART

Artificial leather produced by the conventional production method, i.e.,suitable for a common artificial leather sheet, is widely used forclothing, shoes, gloves and the like because it has a superiorappearance and touch. However, it is inferior in strength and has toohigh an elongation. This makes it difficult to use the sheet to coverfurniture, as a cover sheet for a car chair, for men's clothing and thelike which require a form-stability.

To solve such a problem, there was proposed a method for improvingform-stability by increasing the amount of polyurethane resin to beimpregnated when producing the sheet for artificial leather. In thiscase, the artificial leather achieves excellent form-stability but islow in softness and accordingly, there is a risk that the appearance ofthe artificial leather becomes spoiled.

There was an attempt to decrease the amount of polyurethane resin to beimpregnated to thus improve the appearance and touch of the product whenproducing a sheet for artificial leather. In this case, however, theform-stability of the artificial leather became degraded.

Japanese Patent Laid-Open No. S62-78281 and U.S. Pat. No. 5,256,429disclose a composite sheet for artificial leather which is produced byinserting a layer of fabrics woven from a yarn having more than 1 denierinto a non-woven fabric layer of an ultra fine fiber as a reinforcingmaterial, needle-punching them and physically coupling the ultra finefiber of the non-woven fabric layer and the yarns of the layer of thefabrics.

This method can improve the form-stability of the artificial leather butthere is a problem that the fibers of the layer of the fabrics forreinforcement, which has a much large denier than the ultra fine fiberare raised and protrude to the surface of the composite sheet, thusmaking the touch of the artificial leather rough and hard. Additionally,when performing dyeing, there occurs a difference in dyeingconcentration due to a difference in denier between the ultra fine fiberwhich protrudes to the surface and the thick fiber of the layer of thefabrics for reinforcement, thereby degrading the appearance of theproduct.

As seen from the conventional art, a composite sheet for artificialleather capable of improving the form-stability and touch of theartificial leather has not yet been developed.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a composite sheetused for artificial leather which is very useful for the production ofartificial leather for furniture, cars, men's clothing and sundry goodsbecause it has excellent form-stability and softness.

The present invention provides a composite sheet for artificial leatherwhich has excellent form-stability and softness so that it is suitablefor the production of artificial leather for furniture, cars, men'sclothing and sundry goods. Thus, the present invention provides acomposite sheet for artificial leather which has excellent elongationand softness which has a stitching strength of more than 30 kg/mm, anelongation at constant load of less than 20% and a stiffness of lessthan 80 mm by inserting a woven or knitted fabric constructed from ayarn made of ultra fine fibers having a monofilament denier of less than0.3 into a common sheet for artificial leather composed of a non-wovenfabric layer made of ultra fine fiber and polyurethane resin andneedle-punching the composite.

To achieve the above object, there is provided a composite sheet forartificial leather according to the present invention, comprising: anon-woven fabric layer (1) made of ultra fine fibers having a finenessless than 0.3 denier; a woven or knitted fabric layer (2) constructedfrom a yarn made of ultra fine fibers having a fineness less than 0.3denier; and polyurethane resin, wherein the ultra fine fibers of thenon-woven fabric layer (1) and the ultra fine fibers of the woven orknitted fabric layer (2) are entangled with each other.

Additionally, there is provided a composite sheet for artificial leatheraccording to the present invention, comprising: a non-woven fabric layer(1) made of ultra fine fibers; a woven or knitted fabric layer (2)constructed made of ultra fine fibers; and polyurethane resin, whereinthe ultra fine fibers of the non-woven fabric layer (1) and the ultrafine fibers of the woven or knitted fabric are entangled with each otherand the fineness of the ultra fine fibers of the woven or knitted fabriclayer (2) is not more than the fineness of the ultra fine fibers of thenon-woven fabric layer (1).

Additionally, there is provided a composite sheet for artificial leatheraccording to the present invention, comprising: a non-woven fabric layer(1) made of ultra fine fibers; a woven or knitted fabric layer (2) madeof ultra fine fibers; and polyurethane resin, wherein the ultra finefibers of the non-woven fabric layer (1) and the ultra fine fibers ofthe woven or knitted fabric layer (2) are entangled with each other andthe composite sheet has a stitching strength of more than 30 kg/mm, anelongation at constant load of less than 20% and a stiffness of lessthan 80 mm.

Hereinafter, the present invention will now be described in detail.

Firstly, ultra fine fibers which are employable in the present inventionare made by conjugate-spinning or mix-spinning two kinds of fiberforming polymer materials into a sea-island type or division type, or byordinary-spinning of fiber forming polymer materials to a fineness ofless than 0.3 denier.

In case of the sea-island type, for the island component, polyesterbased polymer or nylon based polymer can be used and, for the seacomponent, copolymer polyester, polyethylene, polyvinyl alcohol,polystyrene and the like which has a solubility in a particular solventdifferent than that of the island component can be used.

In case of the division type, polyester, nylon and copolymer polyestercan be used, which are capable of dividing the ultra fine fibers byextracting or removing one component from two kinds of polymers with asolvent such as sodium hydroxide.

The ultra fine fiber employed in the present invention is formed in twokinds of sheet (layer) form in the composite sheet for artificialleather: one is a staple non-woven fabric layer (1) form and the otheris a woven or knitted fabric layer (2) form.

The staple non-woven fabric layer (1) can be made by cutting a yarn(filament) capable of being fine to a fineness less than 0.3 denier intoshort fibers, then forming a web through a carding-cross lapping processand then needle-punching the same.

The woven or knitted fabric layer (2) can be made by weaving or knittingwith a spun yarn, which is made by carrying out acarding-sliving-twisting process on short fibers (staple) prepared bycutting a yarn (filament) capable of being fine to a fineness less than0.3 denier, or by weaving or knitting with a continuous filament, whichis produced by spin-draw process, through a twisting process. That is,the woven or knitted fabric layer (2) constructed of ultra fine fibersused in the present invention can be woven or knitted from a spun yarnmade of staple or continuous filament yarn.

The ultra fine fibers used in the present invention preferably have afineness less than 0.3 denier after a fiber fining treatment. In a casethat the fineness of the ultra fine fibers is more than 0.3 denier, itis difficult to obtain artificial leather with a soft touch.

Additionally, the yarn constituting the woven or knitted fabric layer(2) in the present invention is more preferably constructed of ultrafine fibers having a fineness of 0.01 to 0.3 denier. Larger fineness maycause damage of the woven or knitted fabric due to a needle-punchingoperation for bonding the woven or knitted fabric (2) to the staplenon-woven fabric layer (1) and the damaged fibers often come out to thesurface of the artificial leather. Thusly, since the fibers of the wovenor knitted fabric layer (2) which come to the surface has a largerfineness than that of the staple fibers of the non-woven fabric layer(1), this brings about an uneven appearance of the artificial leatherand lower softness. Moreover, since the color of the artificial leatheris changed a lot according to the fineness of the fibers after dyeing,the fibers of the woven or knitted fabric layer (2) exposed to thesurface appears to be a conspicuous defect. Furthermore, since a largefineness of fibers can make the touch of the woven or knitted fabriclayer (2) excessively hard, this can spoil the softness of theartificial leather.

The present invention does not specially limit the lowest value of thedenier of the ultra fine fibers constituting the woven or knitted fabriclayer (2). However, in the case that the yarn constructed of excessivelyfine fibers is used for the production of the woven or knitted fabriclayer (2), it is difficult to uniformly control the fineness of theultra fine fibers, the degree of elongation is increased during theprocess after removing the sea component and the physical properties ofthe final product, such as strength, elongation and the like, is largelydecreased, thereby reducing the effect of improving the form-stability.Therefore, the fineness of the ultra fine fibers is more preferably morethan 0.01 denier and less than 0.3 denier.

Additionally, in the present invention, the total denier of the yarnconstituting the woven or knitted fabric layer (2) is preferably 30 to150 denier. Smaller fineness can cause a decrease in physical propertiessuch as strength, elongation and the like, which may bring about adecrease of the form stability. On the other hand, larger fineness canmake the woven or knitted fabric layer (2) excessively hard, and thuslyit is difficult to obtain a desirable softness and flexibility forartificial leather even if it becomes ultra fine after dissolution.

In the present invention, the yarn constituting the woven or knittedfabric layer (2) is preferably constructed of 200 to 10,000 ultra finefibers. After a fiber fining treatment, if the number of the ultra finefibers existing in one strand of the yarn is more than 10,000, thefibers becomes excessively fine or the total denier is increased. Thiseliminates the effect of improving the form stability or increases therisk of losing the softness of the artificial leather, which is notpreferable.

In contrast, if the number of the fibers existing in one strand of theyarn is less than 200 after the fiber fining treatment, the fibersbecomes excessively thick or the total denier is decreased. Thiseliminates the softness or increase the risk of reducing the physicalproperties such as strength, elongation and the like, which is notpreferable.

Moreover, in the present invention, the yarn constituting the woven orknitted fabric layer (2) is preferably a twisted yarn having a number oftwists of 500 to 4000 twist/meter (hereinafter, shown as t/m). If thenumber of twits is 500 to 700 t/m, the form-stability is at an averagelevel but the softness is very excellent. So such a yarn is suitable forartificial leather such as clothing or the like which requires a softtouch.

Further, if the number of twists is 700 to 2,500 t/m, the yarn has a lowelongation and good softness, it is suitable for covering for furniturewhich requires form-stability. On the other hand, if the number oftwists is high, that is, 2,500 to 4,000 t/m, the yarn is more suitablefor artificial leather such as cover sheet for car chairs which requirewear resistance and form-stability.

In case that the woven or knitted fabric layer (2) is a woven fabric,the densities of the warp and weft are more than 40 yarns/inch, morepreferably, more than 60 yarns/inch. The weight of the knitted fabric ispreferably 30 to 200 g/m².

The composite sheet which comprises the non-woven fabric layer (1) ofthe ultra fine fibers combined to the woven or knitted fabric layer (2)can be made by various methods. The most common method is aneedle-punching method wherein one or more staple non-woven fabriclayers and woven or knitted fabric sheets are alternately arranged andare entangled by needle-punching when making a non-woven fabric.

In another method, a woven or knitted fabric sheet of ultra fine fiberscan be bonded with a intermediate product having a non-woven fabric ofultra fine fibers filled with polyurethane resin using an adhesive, or awoven or knitted fabric sheet of ultra fine fibers can be boned with theproduct of which a series of artificial leather treatment such asbuffing or dyeing has been finished.

A 3 to 15% concentration water soluble polymer solution of polyvinylalcohol or carboxylmethyl cellulose is padded and dried on the compositesheet of the non-woven fabric and the woven or knitted fabric so as tohave the amount of 5 to 20% by weight with respect to the weight of thefibers. This process is effective for preventing the touch of the finalproduct from being hard with the polyurethane resin being excessivelyboned with the fibers converted into a bundle of fine fibers in thelater process of impregnating polyurethane resin.

Next, a polyurethane wet impregnating treatment is carried out on thecomposite sheet. The polyurethane elastomer used in this step is easilydissolved in a straight-chained polymer material consisting ofmacroglycol, diisocyanate and a low molecular weight diol or diamine, orin some crosslinking polymer materials such as dimethylformamide(hereinafter, referred to as “DMF”).

The macroglycol used in the present invention may include polyetherglycol, polyester glycol, polyether polyester copolymer glycol,polycarbonate glycol and the like. The low molecular weight diols in thepresent invention may include 4,4′-butandiol, ethylene glycol and thelike. It also may use a chain extender of diamine base such asmethylene-bis-(4,4′-phenylamine).

An impregnating solution is made by adding a detergent, pigments,functional particles and the like to such a DMF solution of polyurethaneelastomer and diluting the resulting solution. The composite sheet isdipped in the impregnating solution, coagulated in an aqueous solution,washed in hot water at 50 to 80° C. for completely removing temporaryfilled water soluble polymer, and then dried. The content of thepolyurethane after drying is preferably 20 to 50% by weight with respectto the weight of the composite sheet.

Continuously, the fibers are converted into a bundle of fine fibers byremoving the sea component from the fiber constituting the non-wovenfabric layer (1) and the woven or knitted fabric layer (2) with asolvent or aqueous solution of sodium hydroxide which is capable ofdissolving the sea-component. The sea component exists in both fibers ofthe non-woven fabric layer (1) and fibers of the woven or knitted fabriclayer (2). If their types of the sea component are different, fiberfining treatment has to be performed to each of them, which makes thetreatment complicated.

Therefore, in the present invention, it is more preferable that thefiber fining treatment is simultaneously attained by only onedissolution process by making the fibers of the non-woven fabric layer(1) and the fibers of the woven or knitted fabric layer (2) from thesame type of the sea component.

In case that the sea component is a copolymerized polyester, the seacomponent is decomposed by a continuous or discontinuous arrangementmethod with a 5 to 15% aqueous solution of sodium hydroxide. In casethat the sea component is polyethylene or polystyrene, the sea componentis removed by treating with toluene, perchloroethylene ortrichloroethylene.

For example, the copolymerized polyester of the sea component iscompletely decomposed and removed by treating with a 10% aqueoussolution of sodium hydroxide at 100° C. for 5 to 10 minutes. At thistime, although the fineness of the composite sheet constructed of thenon-woven fabric layer (1) and the woven or knitted fabric layer (2) isdecreased to some degree because their sea component is simultaneouslyremoved, the form of the composite sheet is kept well by the structureof the woven or knitted fabric, the degree of longitudinal elongationcaused by a mechanical tensile force is not large and the apparentdensity of the surface of the composite sheet is improved.

As seen from the above method, in general, the sea component isdissolved after impregnating with polyurethane. This is referred to aspost dissolution. On the contrary, the sea component can be dissolvedbefore impregnating with polyurethane. This is referred to aspre-dissolution. This method is applied for the purpose of improving theappearance and physical properties of the artificial leather after thefiber fining treatment.

Next, the surface of the thusly obtained composite sheet of the leatherform is buffed by a buffing machine equipped with a sand paper of aproper roughness to thus form raised fibers on the surface and thenfluffs are shagged. The roughness of the sand paper is differentlyselected according to its use. Typically, it is preferable to use thesand paper of 150 to 400 meshes.

The composite sheet for artificial leather with fluffs has the followingcharacteristics from a macrostructual viewpoint. Firstly, on the surfaceformed with the fluffs, there are a small number of filament fibers orspun fibers of the woven or knitted fabric layer (2) broken duringneedle-punching and protruded to the surface. Even if there are somefibers of the woven or knitted fabric layer (2) protruded to thesurface, the fineness is not more than that of the fibers of thenon-woven fabric layer (1).

In case that the fibers of the woven or knitted fabric layer (2)protruded to the surface have a larger fineness than a monofilament ofthe non-woven fabric layer (1), this becomes more apparent after dyeingand their modulus also becomes larger, thereby greatly degrading theappearance and touch of the surface.

Additionally, in the composite sheet for artificial leather of thepresent invention, the weight ratio of the non-woven fabric layer (1) tothe woven or knitted fabric layer (2) is 90:10 to 50:50. Thus, it ispreferable that the weight of the non-woven fabric layer (1) is not lessthan that of the woven or knitted fabric layer (2).

Moreover, in the composite sheet for artificial leather of the presentinvention, the weight ratio of the ultra fine fibers/polyurethane resinis 90:10 to 50:50. Thus, it is preferable that the amount of the ultrafine fibers constituting the non-woven fabric layer (1) and the woven orknitted fabric layer (2) is not less than that of the polyurethaneresin.

The composite sheet for artificial leather having the above-mentionedstructural characteristics is finally treated according to its use.Generally, the composite sheet is made into an artificial leather ofsuede type by a dyeing treatment, or is made into an artificial leatherof mirror-like type by forming a polyurethane coating layer on thesurface.

In case that the composite sheet for artificial leather of the presentinvention is the suede type, the ultra fine fibers located on thesurface has a raised structure.

When directly performing dyeing, in case that the used fiber comprisesnylon-6, it is typically dyed with a metal complex dye or milling typeacid dye. In case of polyester, it is dyed with a disperse dye in a highpressure rapid dyeing machine. Finally, when a softening and functionalagent treatment is carried out on the dyed product, a compositesuede-like artificial leather with excellent surface effect, superiorform-stability and softness is made.

In contrast, in case of making an artificial leather of mirror-like typewith soft surface, no dyeing is performed on the basic fabric withraised fibers, but polyurethane coating is performed on raised fibersusing a typical coating machine for artificial leather. The polyurethaneelastomer used in the above coating process is polyurethane forartificial leather having 20 to 30% solid matter. The coating methodincludes dry or wet coating treatment, if required, laminatingtreatment.

By the above-mentioned procedure and method, it is possible to make acomposite sheet for artificial leather with superior form-stability andsoft touch, i.e., low elongation and excellent softness, and anartificial leather using the same.

As described above, in order to make the composite fiber for artificialleather of the present invention, generally, the woven or knitted fabricsheet made of ultra fine fibers is combined to a non-woven web whenmaking the non-woven fabric. Besides, as shown in the above procedure,it is also possible to bind the woven or knitted fabric sheet made ofthe ultra fine fibers to the product of which a series of artificialleather treatment including dyeing or mirror-like coating treatment hasbeen finished.

In the present invention, various physical properties of the compositesheet for artificial leather are determined as follows.

Fineness (Denier) of Ultra Fine Fiber

The sample of a cross-section of the composite sheet for artificialleather is taken and a preparation process such as gold coating isapplied thereto. The photograph of the surface of the composite sheetfor artificial leather is taken by a scanning electron microscope. Then,the cross-sectional area of the ultra fine fibers shown on thephotograph is evaluated. The cross-sectional area is obtained for eachof ten strands (n=10) of the ultra fine fibers and the average valuethereof is obtained. The obtained value is converted into an actualvalue in consideration of the magnification of the photograph. Then, thefineness is obtained through the following formula.

Fineness (Denier)=9Aρ/1000

In this formula, A is the surface area (μm²) of the cross-section of theultra fine fiber and ρ is the density (g/cm³) of the ultra fine fiber.The applied density of nylon is 1.14 and the applied density ofpolyethylene terephthalate is 1.38.

Here, in case that the cross-section is a circular type, thecross-sectional area A of the ultra fine fiber is obtained by thefollowing formula by measuring the diameter of the cross-section. Incase that the cross section is non-circular type, the cross-section isdirectly obtained through an image analyzer and the like.

In case that the cross-section is a circular type:Cross-section (μm²)=πD ²/4

Number of Ultra Fine Fibers

One strand of yarn constituting the woven or knitted fabric layer (2) istaken from the prepared composite sheet for artificial leather and apreparation process such as gold coating is applied thereto. Then, thephotograph of the cross-section of one strand of yarn constituting thewoven or knitted fabric layer (2) is taken by a scanning electronmicroscope and the number of ultra fine fibers shown on the photographis counted.

Stitching Strength

Two test pieces each having a width of 100 mm and a length of 100 mm areprepared, respectively, in the longitudinal and transverse directions ofthe composite sheet for artificial leather. One end of a test piece, isoverlaid on the one end of another test piece. And then sewing (*) afolded part, which is 10 mm from the ends of each test piece so as toform two groups of test pieces, respectively, in the longitudinal andtransverse directions. The stitching strength is measured under theconditions of a clamp distance of 76.2 mm (3 inches), a clamp size of a20 mm length and a 30 mm width for both upper and lower portions and apulling speed of 200 mm/min. The measurements in the two directions areaveraged and reported herein as the “stitching strength” of thecomposite sheet in kg of overhang per mm of composite sheet fineness.

* A high tenacity nylon yarn is used as the sewing yarn and the sewingdistance is 4 mm. Among common sewing yarns, the high tenacity nylonyarn has a high strength of about 200 denier. It must have a largertension strength than those of the test pieces and must not change thetest result. In addition, the stitches at the opposite ends have to betightly knotted by sewing it with a sewing yarn that is cut to aslightly large length, so that it cannot be loosened.

Elongation at Constant Load

Three test pieces each having a width of 50 mm and a length of 250 mmare cut out from the composite sheet for artificial leather in thelongitudinal and transverse directions and a standard length of 100 mmis marked along their center lines. These test pieces are mounted on afatigue tester (*) at a clamp distance of 150 mm and a 8 kg load(including the load of the lower clamp) is carefully suspended on thetest pieces for 10 minutes. With the load being suspended for 10minutes, the standard length (l₀) is obtained and the elongation atconstant load is calculated by the following formula;Elongation at constant load (%)=l ₀−100

In this formula, l₀ designates the standard length (mm) after suspendingthe load of 8 kg for ten minutes. * As the fatigue tester, ‘Marlensfatigue tester’ is used.

Stiffness

Five test pieces, each having a 25 mm width and a 200 mm length, aretaken out of a sample, respectively, in the longitudinal and transversedirections. The test pieces are placed on a smooth horizontal tablehaving a 45 degree inclined surface at its pointed end and a scale atits top surface so that the shorter side of the test pieces matches thebase line of the scale. Then, the test pieces are pressed by a pressingplate of the same size as the test pieces and are slid toward theinclined surface at a speed of approximately 10 mm/sec, and when the oneend of the test pieces contacts the inclined surface, the position ofthe other end of the test pieces is read by the scale. The stiffness isindicated by the moving distance (mm) of the test pieces from the baseline. The stiffness is measured both for the front surface and for thebackside of each test pieces, and expressed in an average obtained fromthe measurements made for the front surface and backside of five testpieces, respectively, in the longitudinal and transverse directions.

Surface State (Appearance/Color Difference)

The surface state is evaluated by 10 panelists. The surface state judgedby more than 8 persons to be good was designated as “⊚”; the case wheresix or seven persons judged the surface state to be good was designatedas “⋄”; the case where four or five persons judged the surface state tobe good was designated as “Δ”; and the case where three or less personsjudged the fabric to be good was designated as “x”.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of preferredembodiments of the present invention will be more fully described in thefollowing detailed description, taken accompanying drawings. In thedrawings:

FIG. 1 is a scanning electron micrograph of a cross-section of acomposite sheet for artificial leather of the present invention;

FIG. 2 is a schematic view of the cross-section of the composite sheetfor artificial leather of the present invention wherein the denier ofultra fine fibers of a woven or knitted fabric layer (2) is smaller thanthat of ultra fine fibers of a non-woven fabric layer (1);

FIG. 3 is a schematic view of the cross-section of the composite sheetfor artificial leather of the present invention wherein the denier ofthe ultra fine fibers of the woven or knitted fabric layer (2) is thesame as that of the ultra fine fibers of the non-woven fabric layer (1);and

FIG. 4 is a schematic view of the cross-section of the composite sheetfor artificial leather of the present invention wherein the denier ofthe ultra fine fibers of the woven or knitted fabric layer (2) is largerthan that of the ultra fine fibers of the non-woven fabric layer (1).

※ Explanation of reference numerals for main parts of the drawings

1: non-woven fabric layer made of ultra fine fibers

1 a: ultra fine fibers of non-woven fabric layer

2: woven or knitted fabric made of ultra fine fibers

2 a: ultra fine fibers of woven or knitted fabric having a smallerdenier than ultra fine fibers of non-woven fabric layer

2 b: ultra fine fibers of woven or knitted fabric having the same denieras ultra fine fibers of non-woven fabric layer

2 c: ultra fine fibers of woven or knitted fabric having a larger denierthan ultra fine fibers of non-woven fabric layer

3: area having a combination of ultra fine fibers and polyurethane resin

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail withreference to examples, but not limited thereto.

Example 1

A sea-island type composite continuous fiber having a fineness of 3deniers convertible into a bundle of fine fibers was prepared from 70 byparts weight of polyethylene terephthalate as a fiber-forming componentand 30 parts by weight of copolymer polyester as an extraction componentthrough spinning and drawing processes. At this time, the monofilamentof the continuous fiber has 16 ultra fine fibers (fiber-formingcomponent) therein. A part of the thusly obtained composite fiberconvertible into a bundle of fine fibers was used to produce shortfibers by cutting it out at a 40 mm length and giving a crimp. Anotherpart thereof was used as warp and weft in producing a woven fabric whichhad a warp density of a 100 yarns/inch, a weft density of 80 yarns/inchand a weight of 100 g/yd after twisting it in the form of continuousfibers with a total fineness of 75 deniers at 2500 twists per meter in atwisting machine. The above-mentioned short fibers formed a web by acarding-cross lapping process, and this web was combined to the wovenfabric by needle-punching during the preparation of a non-woven fabric,thereby forming a composite sheet. Then, the composite sheet of thenow-woven fabric layer and the woven fabric layer was padded and driedin a 10% aqueous solution of polyvinyl alcohol so as to have the amountof 10% by weight with respect to the weight of the fibers. Afterwards,the composite sheet was dipped in a 15% impregnating solution preparedby diluting a polyurethane elastomer of the polyether-polyestercopolymer glycol type in dimethylformamide (DMF). Then, the polyurethanewas coagulated in the aqueous solution, washed in a 70° C. hydrothermalsolution for removing polyvinyl alcohol polymer, and dried. The contentof polyurethane after the drying step was found to be 25% by weight. Thecomposite sheet constructed of the above-mentioned fibers andpolyurethane was converted into a bundle of fine fibers by continuouslytreating it in a 10% aqueous solution of sodium hydroxide at 100° C. forcompletely removing the sea component, i.e., copolymer polyester, sothat only the island component, i.e., the component of polyester finefibers, was left. At this time, both the fibers in the non-woven fabriclayer and the ultra fine fibers in the woven fabric layer had a finenessof 0.13 denier and the number of ultra fine fibers constituting thefilament of woven fabric was 400. Then, a part of the ultra fine fiberswas cut out and raised by carrying out buffing treatment using a #240grit sand paper in order to obtain fluffs. Next, the obtained sheet wasdyed with a disperse dye having an excellent fastness in a high pressurerapid dyeing machine. Then the sheet was reduction, cleared, and dried.Continuously, water repellent and antistatic agent treatment and flufftip softening treatment were carried to thus prepare a suede-likecomposite sheet for artificial leather. The physical properties of thethus obtained composite sheet for artificial leather were evaluated andthe result was shown in Table 2.

Examples 2 to 5

Except that the denier of ultra fine fibers of a non-woven fabric, thenumber of ultra fine fibers of a yarn constituting a woven fabric, thenumber of twists of the yarn constituting the woven fabric, and thedenier of ultra fine fibers of the yarn constituting the woven fabricare changed as in Table 1, a composite sheet for artificial leather wasprepared in the same manner as that in EXAMPLE 1. The physicalproperties were evaluated and shown in Table 2.

TABLE 1 Preparation Conditions Filament of woven fabric Denier of ultrafine Denier fibers in non-woven of ultra Number of Number of fabric(denier) fine fibers ultra fine fibers twists Example 1 0.13 0.13 4002,500 Example 2 0.15 0.07 900 2,000 Example 3 0.07 0.07 3,600 1,000Example 4 0.07 0.04 900 600 Example 5 0.20 0.13 1,500 3,000

Comparative Example 1

Except that a polyester multifilament of 75 deniers/24 filaments(monofilament denier: 3.16 denier) was used as the warp and weft of awoven fabric, a composite sheet for artificial leather was prepared inthe same manner as that in Example 1. The physical properties wereevaluated and shown in Table 2.

Comparative Example 2

Except that a polyamide multifilament of 75 deniers/24 filaments(monofilament denier: 3.16 denier) was used as the warp and weft of awoven fabric, a composite sheet for artificial leather was prepared inthe same manner as that in Example 1. The physical properties wereevaluated and shown in

TABLE 2 Result of Evaluation of Physical Properties Stitching Elongationat Surface State Strength Constant Load Stiffness (Appearance, (kg/m)(%) (mm) Color Difference) Example 1 65 3.5 49 ⊚ Example 2 62 4.8 42 ⋄Example 3 61 7 38 ⊚ Example 4 48 12 27 ⋄ Example 5 45 2.7 58 ⋄Comparative 59 5 86 X Example 1 Comparative 25 22 73 Δ Example 2

INDUSTRIAL APPLICABILITY

As the composite sheet for artificial leather of the present inventioninclude a woven or knitted fabric layer (2) composed of a yarn of ultrafine fibers having a fineness less than 0.3 denier and the ultra finefibers of woven or knitted fabric layer (2) being entangled with theultra fine fibers of a non-woven fabric layer (1), it is low inelongation and superior in form-stability.

Regarding the form-stability, the composite sheet for artificial leatherof the present invention has an elongation at constant load of less than20% and thus a form change is not occurred much. Additionally, thestitching strength is more than 30 kg/mm and thus shows very strong andwear resistant stitching characteristics. Therefore, the composite sheetfor artificial leather of the present invention is very suitable for theproduction of cover sheet of a car chair and covering for furniturewhich require superior form-stability and stitching characteristics, andartificial leather for men's clothing which require relatively strongand highly wear resistant.

Moreover, both the fibers of the non-woven fabric layer (1) constitutingthe composite sheet for artificial leather of the present invention andthe fibers of the woven or knitted fabric layer (2) are composed ofultra fine fibers of less than 0.3 denier, and thus are superior insoftness. Regarding softness, the composite sheet for artificial leatherof the present invention has a stiffness of less than 80 mm and thus isvery soft.

Therefore, since the composite sheet for artificial leather of thepresent invention is excellent in both form-stability and softness, itis very useful for all kinds of leather including natural leather,artificial leather and synthetic leather as well as for cover sheet of acar chair, covering for furniture and clothing.

1. A method of manufacturing a composite sheet for artificial leather,the method comprising: providing a sea-island, non-woven fabric layerconsisting of composite short fibers having a sea component and anisland component, said composite short fibers having a fineness of lessthan 0.3 denier; extracting the sea component from the island componentof the sea-island non-woven composite short fibers; providing asea-island woven or knitted composite filament having a sea componentand an island component, said composite filament having a fineness notmore than the fineness of the island component of the non-wovencomposite short fiber after said extracting of the sea component ofnon-woven composite short fiber; needle punching the non-woven compositeshort fibers with the woven or knitted composite filament to form amanufactured composite sheet and impregnating the manufactured compositesheet with a polyurethane solution, coagulating the impregnatedcomposite sheet in an aqueous solution, and extracting sea componentsexisting in the coagulated composite sheet.
 2. A method of manufacturinga composite sheet for artificial leather, the method comprising:providing a sea-island, non-woven fabric layer consisting of compositeshort fibers having a sea component and an island component, saidcomposite short fibers having a fineness of less than 0.3 denier;extracting the sea component from the island component of the sea-islandnon-woven composite short fibers; providing a sea-island woven orknitted composite filament having a sea component and an islandcomponent, said composite filament having a fineness not more than thefineness of the island component of the non-woven composite short fiberafter said extracting of the sea component of non-woven composite shortfiber; needle punching the non-woven composite short fibers with thewoven or knitted composite filament to form a manufactured compositesheet; and impregnating the manufactured composite sheet with apolyurethane solution, coagulating the impregnated composite sheet in anaqueous solution, and extracting sea components existing in thecoagulated composite sheet, wherein the weight ratio of the compositeshort fibers that have a fineness of less than 0.3 denier to thepolyethylene is 90:10 to 50:50, and the composite sheet has a stitchingstrength of greater than 30 kg/mm.